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Reuse of Aqueous Waste Streams in Transportation-Related Applications

Aqueous waste streams can be produced from many commercial,
industrial, and municipal processes or activities. Proper management,
treatment and disposal or reuse of these waste streams are necessary
to conserve natural resources and reduce their environmental impacts.
In South Dakota, aqueous waste streams generating processes include
municipal water and wastewater treatment, oil and gas production,
ethanol production, food processing (cheese, meat and others), and
other industrial processes (ion exchange, reverse osmosis, etc.). These
aqueous waste streams can be recycled or reused to reduce the
demand on natural water resources. Beneficial reuse of these waste
streams will save the cost of waste treatment and disposal, reduce the
consumption of natural resources, and minimize the environmental
impacts.
Aqueous waste streams have been used by transportation agencies as
alternative anti-icing and deicing materials and dust suppressants on
unpaved roads to reduce maintenance costs (USEPA, 2002; Michigan
DEQ, 2002; Federal Highway Administration, 2013). This practice
also reduces the costs associated with management, treatment and
disposal of the waste materials. Most departments of transportation
(DOTs) rely on chloride-based anti-icing and deicing compounds for
treating roadways during winter weather events to ensure the safety
of transportation. The most common chloride-based compound is
sodium chloride (rock salt). Magnesium chloride and calcium
chloride are also frequently used. The traditional method of
pavement deicing is applying dry, granular rock salts and sands to the
roadway during the storm event. In recent years, there has been
growing interest in using salt brine as an anti-icing compound
(Minnesota DOT, 2013). Pre-wetting using salt brines has been
shown to increase the performance of salts and abrasives, as well as
their longevity on the roadway surface, thereby reducing the amount
of materials required (Levelton, 2007; Minnesota DOT, 2012).
Oil-field brine is a saline byproduct that is generated during oil and
gas drilling, completion, and production operations. This salt brine is
permitted by Michigan, New York, North Dakota, Ohio,
Pennsylvania, and other states for snow and ice control. Oil-field
brine has been proven to be an effective pretreatment for winter
storms (Ohio DNR, 2004). Other aqueous waste streams that have
been used as anti-icing and deicing agents include corn wet-milling
waste byproducts, cheese brewing waste, beer brewing waste, beet
juice and others (Iowa DOT, 2010). In Polk County, Wisconsin,
liquid cheese brine has been used to mix with rock salts and pre-wet
the roadway surface since 2008, which results in approximately 30%
reduction in salt usage.
Aqueous waste streams can also be used to control dust on unpaved
roads, construction sites and agricultural fields (Federal Highway
Administration, 2013). Transportation agencies use dust suppressants
to control erosion and reduce maintenance costs on unpaved roads.
Materials used as dust suppressants include water, salts, asphalt
emulsion, vegetable oils, molasses, synthetic polymers, mulches, and
lignin products (USEPA, 2002). Many of the dust suppressants are
formulated with waste products recycled from other industries.
Approximately 75-80% of all dust suppressants used by
transportation agencies are chloride salts and salt brine products
(Travnik, 1991). These salt products stabilize the soil surface by
absorbing moisture from the atmosphere. Oil-field brine has also been
used as a cost effective dust suppressant and road stabilizer, and its
efficiency for dust control has been well recognized (Pennsylvania
DEP, 2015).
Lime sludge is another waste stream that can be potentially used for
transportation-related applications. Lime sludge is produced by the
lime softening treatment process where lime is added to the water to
reduce the hardness. Disposal of lime sludge remains a major
challenge to many municipalities in the Midwest. Lime sludge may
be potentially used on gravel roads to reduce dust generation and
used as an aggregate in cement production (Iowa DOT, 2004).
Overall, waste brine and other aqueous waste streams have been used
by many state DOTs for transportation-related applications. The
experiences of these state DOTs suggest that salt brine solutions can
be effective ice control agents and dust suppressants. When
application rate and volumes are properly controlled, waste brine can
be spread on roadways with minimum environmental risks.
The Watertown Municipal Water Treatment Plant operates a
magnetic ion exchange (MIEX) system to treat its source water. The
MIEX system produces brine wastewater that requires proper
treatment and disposal. The City currently discharges the waste
stream into a lime sludge pit. The dewatered solids are eventually
disposed of in the landfill. The City is evaluating other alternatives to
landfilling to reduce the cost of disposal. The brine wastewater
produced by the MIEX system is expected to have similar salinity as
other salt brine solutions that have been used for ice and dust control.
Therefore, the MIEX brine may be used by transportation agencies in
South Dakota for winter road maintenance and dust control on
unpaved roads. Beneficial reuse of the salt brine will reduce costs of
disposing and treating waste materials and purchasing new materials,
and lead to more sustainable operations at state and local highway
departments and municipal utilities.
Beneficial reuse of waste streams in transportation applications
requires a comprehensive evaluation of the benefits and risks, and
this depends on several major factors including the effectiveness,
safety, economics, environmental benefits and risks, and local, state,
and federal regulations associated with transportation-related
applications of the waste streams. Guidance should be developed to
help state and local agencies determine how to evaluate waste streams
for potential reuse in transportation applications and establish sound
procedures to manage their reuse.